is examined? Is it entirely different from everything else? It is a
fact of common knowledge that the human body is supported by a bony axis,
the vertebral column, to which the skull is articulated and to which also
the skeletal framework of the limbs is attached. These characteristics
place man inevitably among the so-called vertebrata; he is certainly not
an invertebrate, nor is the basic structure of his body such that a third
group, outside the invertebrata and vertebrata, can be made to include
only the single type--man.

Passing now to the classes that make up the group of vertebrates, we meet
first the lampreys or cyclostomes without jaws, and the others with jaws,
such as the fishes, amphibia, reptiles, birds, and mammals, each class
distinguished by certain definite characters in addition to the vertebral
column. The fishes have gills and scales; amphibia of to-day are
scaleless, and they are provided with gills when they are young and lungs
as adults; reptiles have scales and lungs; birds are warm-blooded and
feathered; while mammals are warm-blooded and haired. Is the human species
a unique kind of vertebrate, or does it find a place in one of these
classes? The occurrence of hair, of a four-chambered heart which propels
warm blood, of mammary glands, and of other systematic characters marks
this species as a kind of mammal and not as a vertebrate in a section by
itself.

The members of the class mammalia differ much among themselves; and now
that we recognize clearly that man is a mammalian vertebrate, the next
question is whether an order exists to which our type must be assigned, or
whether we have at last reached a point where it is justifiable to
establish an isolated division to contain the human species alone. We are
familiar with many representatives of different mammalian orders and with
the kind of structural characteristics that serve as convenient
distinctions in denoting their relationships. Horses and cattle, sheep,
and goats and pigs resemble one another in many respects besides their
hoofs, and they form one natural order; the well-developed gnawing teeth
of rats and rabbits and squirrels place these forms together in the order
rodentia; the structures adapting their possessors for a flesh-eating and
predatory life unite the tribes of the lion, wolf, bear, and seal, in the
order carnivora. Among these and other orders of mammalia is one to which
the lemurs, monkeys, and apes are assigned, bec